Photodegradation response of PP and PETG composites

This work revisits the accelerated weathering behavior of polymer composites, with a particular focus on the differential responses observed between their surface and core regions. For this purpose, two distinct long glass fiber reinforced polymer (FRP) systems are chosen with polypropylene (PP) and polyethylene terephthalate with glycol modification (PETG) as matrices. Through a series of controlled (accelerated) weathering experiments and characterization, the study examines the variations in molecular weight, extent of degradation in mechanical and thermal properties of these composites across the thickness (from surface to core regions). Photo-oxidation is the main mode of degradation observed in both composites and is restricted to the exposed surface regions irrespective of the weathering duration employed in the current study. Significant reductions in molecular weight are seen for both composites at the exposed surface regions independent of their chemical nature (∼34% and ∼55% in PP and PETG composites, respectively, by week 19). This further has a noticeable influence on the thermal properties of these composites at the surface regions (in terms of their onset degradation temperatures). In PETG-based composites, despite their notable susceptibility to water ingress during the weathering period, there is no discernible hydrolytic degradation. However, the negative impact on bulk mechanical properties is evident due to water ingress. In contrast, PP composites exhibit no observable changes in bulk mechanical properties. These findings offer valuable insights into the long-term performance and the impact on service life of these composites, facilitating the selection of suitable materials for specific applications.